KR20150048068A - Fabricating method of electrode for electrochemical device, electrode slurry, and electrode for electrochemical device fabricated thereby - Google Patents

Abstract

The present invention provides a manufacturing method of an electrode for an electrochemical device, and an electrode slurry and an electrode for an electrochemical device which are manufactured by the manufacturing method of an electrode for an electrochemical device. More specifically, the manufacturing method of an electrode for an electrochemical device comprises the steps of: dispersing a graphene oxide into a solvent to manufacture a graphene oxide solution; mixing the graphene oxide solution with an active material to manufacture an electrode slurry; applying the electrode slurry to a substrate; and drying the applied electrode slurry to form an electrode active material layer. Accordingly, through the manufacturing method of an electrode for an electrochemical device, a bonding strength between active materials or between the active material and the substrate can be enhanced without using a polymer binder. Also, the polymer binder is not used, thereby improving energy density of the electrochemical device. Furthermore, the efficiency of the electrochemical device can be improved and the lifetime of the device can be extended due to the generation of a reduced graphene oxide.

Description

TECHNICAL FIELD [0001] The present invention relates to a method for manufacturing an electrode for an electrochemical device, an electrode slurry for an electrochemical device, and an electrode for an electrochemical device,

The present invention relates to an electrochemical device, and more particularly, to a method of manufacturing an electrode for an electrochemical device including a graphene oxide, an electrode slurry for an electrochemical device, and an electrode for an electrochemical device.

The electrode of a lithium secondary battery, which is one of electrochemical devices, is manufactured by a method of applying a slurry of an anode / cathode electrode to a conductive substrate (current collector) and drying it. Generally, in a lithium secondary battery, after the electrons existing in the anode / cathode are injected into the cathode / anode, the electrons are combined with the lithium ion, so that the battery is driven in such a manner that the battery is charged and discharged. Therefore, the improvement in the bonding force between the electrode and the current collector is closely related to the improvement in the lifetime and the rate characteristics of the battery. Specifically, this is highly related to the production of an electrode for an electrochemical device including a step of applying an electrode slurry to a current collector, and research on this has been continuously carried out.

Conventionally, an electrode slurry was prepared by mixing an active material, a polymer binder, and conductive particles in water or an organic solvent, and dispersing the mixture to form an electrode slurry. Thus, the prior art attempts to improve the bonding between the active materials in the electrode slurry or the bonding between the active material and the conductive particles by adding a polymer binder to the electrode slurry. However, since most of the polymer binders are electrically nonconductive, there is a problem that when a certain amount or more is added, the movement of electrons in the electrode is inhibited, the efficiency of the electrochemical device containing the same is lowered, or the life of the battery is shortened.

Generally, since the polymer binder and the conductive particles are electrochemically inert, there is a disadvantage that the energy density of the lithium secondary battery is lowered by adding the polymer binder and the conductive particles.

SUMMARY OF THE INVENTION The present invention has been made in order to solve the above-mentioned problems, and it is an object of the present invention to provide a method of manufacturing an electrode slurry, which does not require addition of a polymer binder to an electrode slurry used for electrode formation, A method for manufacturing an electrode for an electrochemical device, an electrode slurry for an electrochemical device, and an electrode for an electrochemical device.

According to an aspect of the present invention, there is provided a method for manufacturing a thin film transistor, comprising: preparing a graphene oxide solution by dispersing graphene oxide in a solvent; preparing an electrode slurry by mixing the graphene oxide solution and an active material; And drying the coated electrode slurry to form an electrode active material layer. The present invention also provides a method for manufacturing an electrode for an electrochemical device, comprising:

The graphene oxide may comprise an oxygen functional group.

And further adding a reducing agent to the graphene oxide solution.

The reducing agent may be at least one selected from the group consisting of hydrazine, hydroic acid, and sodium borohydride.

The slurry may not contain a polymeric binder.

In the step of preparing the slurry by mixing the graphene oxide solution and the active material, the active material and the graphene oxide may be mixed in a weight ratio ranging from 92: 8 to 88:12.

In the step of forming the electrode active material layer by drying the applied electrode slurry, a part of the applied graphene oxide may be reduced to form reduced graphene on the surface of the electrode active material layer.

Another aspect of the present invention is an electrode slurry for an electrochemical device, comprising an active material, a solvent, and a graphene oxide, wherein the active material and the graphene oxide are mixed in a weight ratio ranging from 92: 8 to 88:12. Can be provided.

The electrode slurry may not include a polymeric binder.

Another aspect of the present invention can provide an electrode for an electrochemical device including an active material and a graphene oxide binder.

And the reduced graphene may be formed on at least one surface of the graphene oxide binder.

According to the method for manufacturing an electrode for an electrochemical device of the present invention, the bonding force between the active materials or the bonding force between the active material and the substrate (collector) can be improved without using the polymeric binder.

Further, since the polymeric binder is not used, the energy density of the electrochemical device can be improved.

In addition, the reduction of the electrochemical device by the generation of the reduced graphene can extend the life of the device.

1 is a SEM photograph of a graphene oxide powder according to an embodiment of the present invention.
2 is an SEM photograph of a Si-Ni-Ti metal alloy powder as a silicon-based anode active material.
3 is a graph showing the results of evaluating the rheological behavior of the negative electrode slurry according to the ratio of the graphene oxide and the negative electrode active material made of the Si-Ni-Ti metal alloy.
4 is an image showing the dispersion stability of a graphene oxide solution to which a reducing agent is added according to an embodiment of the present invention.
5 (a) to 5 (b) are graphs showing results of FT-IR analysis of a graphene oxide solution prepared according to an embodiment of the present invention and a graphene oxide solution added with a reducing agent.
6 is an SEM photograph showing the result of observing the surface of the electrode according to the ratio of the anodic active material made of a Si-Ni-Ti metal alloy and the graphene oxide.
FIGS. 7 (a) to 7 (c) are graphs showing characteristics and results of a lithium secondary battery according to an embodiment of the present invention.

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. However, the present invention is not limited to the embodiments described herein but may be embodied in other forms. Like reference numerals designate like elements throughout the specification.

Manufacture of electrodes for electrochemical devices

First, a graphene oxide solution is prepared by dispersing a graphene oxide in a solvent.

In order to prepare a graphene oxide solution, a graphene oxide is prepared. The graphene oxide may be prepared using the Hummers method. The graphene oxide may be prepared in the form of a nano sheet. At this time, the graphene oxide may have a lateral dimension of 100 nm to 100 탆, but the present invention is not limited thereto.

The graphene oxide may comprise an oxygen functional group. Specifically, the graphene oxide may include an oxygen functional group such as a hydroxyl group, an epoxide group, a carboxyl group, and a lactate group. Thus, when the graphene oxide is prepared in the form of a nanosheet, the oxygen functional group can be disposed on the surface of the nanosheet. By the action of the oxygen functional groups contained in the graphene oxide, the graphene oxide can be easily dispersed in the solvent when forming the graphene oxide solution described later.

The preparation of the graphene oxide solution can be accomplished by a simple process of mixing the graphene oxide in the solvent. At this time, any solvent that can disperse the graphene oxide may be used as the solvent, but a solvent capable of preventing the adverse effect of the residual organic solvent on the cell can be used. In one embodiment of the present invention, water may be used as the solvent.

Further, in one embodiment of the present invention, a reducing agent may be further added to the graphene oxide solution. Specifically, in order to form a reduced graphene on at least one surface of the electrode active material layer by reducing the graphene oxide contained in the graphene oxide solution in a step of forming an electrode active material layer described later .

The reducing agent may be at least one selected from the group consisting of hydrazine, hydroic acid, and sodium borohydride.

Specifically, when the reducing agent is added to the graphene oxide solution, the graphene oxide contained in the graphene oxide solution may be added in an amount of 15 g or more based on 1 mL of the reducing agent. This may be for the dispersion stability of the graphene oxide solution, and will be described in detail below with reference to the following experimental examples and drawings.

Thereafter, the graphene oxide solution and the active material are mixed to prepare an electrode slurry.

In this case, LiMO ₂ (M = V, Cr, Co, Ni), LiM ₂ O ₄ (M = Mn, Ti, V), LiMPO ₄ Can be selected from various material groups such as _1-x Co _x O ₂ (0 <x <1), LiNi _2-x Mn _x O ₄ (0 <x <2) and Li [NiMnCo] O ₂ , Depending on the active material, the cathode active material may have a layered structure, a spinel structure or an olivine structure. The anode active material may be a carbon material such as graphite or hard carbon or a metal material such as Li, Na, Mg, Al, Si, In, Ti, Pb, Ga, Ge, Sn, Bi, Sb, ₄ Ti ₅ O _12, and the like. Specifically, the negative electrode active material may be one using, for example, graphite, silicon, germanium, tin, lithium titanate, TiO ₂ , SnO ₂ , ITO, SiO _x , or a mixture thereof. In one embodiment of the present invention, the negative electrode active material may be a material made of a Si-Ni-Ti metal alloy, but the positive and negative electrode active materials usable in the present invention are not particularly limited.

The electrode slurry may be prepared by a simple process of mixing the active material with the graphene oxide solution.

In one embodiment of the present invention, the concentration of the graphene contained in the electrode slurry may be 1 mg / mL to 10 mg / mL.

In addition, when the electrode slurry is prepared, the binding between the active materials contained in the electrode slurry can be controlled by controlling the mixing ratio of the active material (cathode active material or anode active material) and the graphen oxide. Also, the viscosity of the electrode slurry for the electrochemical device can be controlled by controlling the mixing ratio of the active material and the graphene oxide. For example, when the electrode slurry is prepared, the active material (cathode active material or anode active material) and the graphene oxide contained in the graphene oxide solution may be mixed in a weight ratio ranging from 50:50 to 99: 1. Specifically, in one embodiment of the present invention, the active material and the graphene oxide contained in the graphene oxide solution may be mixed in a weight ratio ranging from 92: 8 to 88:12. When mixed at the ratio within the above range, the electrode slurry optimized for the electrode of the electrochemical device can be produced.

Further, in one embodiment of the present invention, the electrode slurry may not include a polymer binder. Even if the electrode slurry does not include the polymer binder, it is possible to provide sufficient bonding force between the active materials by the graphen oxide contained in the slurry.

Then, the electrode slurry is coated on the substrate.

The substrate serves as a collector, and aluminum or stainless steel is preferably used as the substrate of the anode, but not limited thereto. In addition, when used as a current collector for a negative electrode, copper or stainless steel is preferable, but not limited thereto. When the electrode slurry is coated on the substrate, the coating can be performed using a gravure coating method, a slit die coating method, a knife coating method, or a spray coating method.

A bonding force between the active material contained in the electrode slurry and a bonding force between the substrate coated with the slurry and the bonding force between the substrate coated with the slurry and the bonding force between the substrate and the substrate coated with the slurry, The bonding force with the active material in the slurry can be improved. Accordingly, the present invention can improve the problems caused by the use of the conventional polymer binder because the graphene oxide can act as a binder without using the electrochemically inert polymer binder.

Finally, the coated electrode slurry may be dried to form an electrode active material layer.

The drying step may be performed at a temperature of 100 ° C to 120 ° C. At this time, the drying step may be performed in a vacuum atmosphere, or in an atmosphere filled with hydrogen (H ₂ ), ammonia (NH ₃ ), or argon (Ar). The electrode active material layer may be formed on the substrate through the drying process. At this time, in the step of drying the applied electrode slurry, a part of the applied graphene oxide may be reduced to form reduced graphene on at least one surface of the electrode active material layer. However, the present invention is not limited thereto, The entire electrode active material layer may be reduced. Specifically, in the drying process, a part of the graphene oxide is reduced on the surface of the applied electrode slurry, and the oxygen functional groups contained in the graphene oxide are removed, so that the graphene oxide contained in the electrode active material layer is reduced It can be changed to a pin. Accordingly, the electron mobility is increased, and the electrical conductivity of the electrochemical device can be improved. That is, as a result, an active material and a graphene oxide binder may be formed on the substrate, and reduced graphene may be formed on a part of the surface of the graphene oxide binder.

Thereafter, an electrode for an electrochemical device according to an embodiment of the present invention can be manufactured through a pressing process. Thereafter, the substrate is removed to obtain a free standing film containing the electrode active material layer, the graphene oxide binder, and the reduced graphene, and may be used as an electrode of the electrochemical device. The electrode of the electrochemical device can improve the lifetime characteristics of the electrochemical device by facilitating the electron transfer due to the improvement of the hygroscopic property and the electric conductivity of the electrolyte using the hydrophilic property of the graphene oxide.

Manufacture of electrochemical devices

The electrochemical device may further include an anode, an anode, and an electrolyte disposed between the anode and the cathode, wherein at least one of the anode and the cathode includes an electrode for an electrochemical device including a graphene oxide . The electrolyte may be a liquid electrolyte or a polymer electrolyte. When the electrolyte is a liquid electrolyte, the separator may further include a porous membrane between the anode and the cathode.

Such an electrochemical device is expected to be applicable to a field of energy production and storage, for example, a lithium secondary battery, a super capacitor, or a hybrid type energy storage device between a super capacitor and a secondary battery.

Hereinafter, exemplary embodiments of the present invention will be described in order to facilitate understanding of the present invention. It should be understood, however, that the following examples are intended to aid in the understanding of the present invention and are not intended to limit the scope of the present invention.

&Lt; Experimental Example 1: Preparation of graphene oxide powder >

A graphene oxide powder was obtained from the graphite particles using the Hummers method. Thereafter, the structure was observed using a scanning electron microscope (SEM).

1 is a SEM photograph of a graphene oxide powder according to an embodiment of the present invention.

Referring to FIG. 1, it can be seen that graphene oxide nanosheets having a side dimension of 100 nm to 100 μm are well formed.

Experimental Example 2: Preparation of a graphene oxide solution [

0.7 g of the graphene oxide powder prepared in Experimental Example 1 was added to 100 mL of secondary distilled water and dispersed for 1 hour using a bath sonicator. The mixture was stirred for an additional 24 hours using a stirrer to maintain uniform dispersion of the prepared graphene oxide solution.

&Lt; Experimental Example 3: Preparation of electrode slurry >

An electrode slurry was prepared by mixing a silicon-based anode active material composed of Si-Ni-Ti metal alloy with the graphene oxide solution prepared in Experimental Example 2. Wherein the negative active material and the graphen oxide contained in the graphen oxide solution have a composition of 97.5: 2.5, 94: 6, 92: 8, 91: 9, 90:10, 89: 11, 88:12, and 80:20, respectively, to prepare respective electrode slurries.

&Lt; Analysis Example 1: Evaluation of rheological behavior of electrode slurry >

The viscosity behavior of the electrode slurry was investigated by increasing the shear rate under constant shear stress.

2 is an SEM photograph of a silicon-based negative electrode active material made of a Si-Ni-Ti metal alloy.

Referring to FIG. 2, it can be seen that the silicon-based anode active material is uniformly distributed.

3 is a graph showing the results of evaluating the rheological behavior of the negative electrode slurry according to the ratio of the graphene oxide and the negative electrode active material made of the Si-Ni-Ti metal alloy.

Referring to FIG. 3, it can be seen that a shear thinning phenomenon occurs in which the viscosity decreases as the shear rate increases. Specifically, the prepared electrode slurry had a high viscosity of 106 mPa · s or more at a low shear rate (10 ^-3 1 / s) and a high viscosity of 10 100 mPa · s at a high shear rate (10 ² 1 / s) mPa · s. This means that the prepared electrode slurry has excellent flowability at a high shear rate at which the electrode slurry is applied in an actual process, and that the formed coating layer can be well maintained immediately after the application.

EXPERIMENTAL EXAMPLE 4: Preparation of a graphene oxide solution to which a reducing agent was added:

The graphene oxide powder prepared in Experimental Example 1 was divided into 3 g, 3.75 g, 5 g, 7.5 g and 15 g, respectively, in 1 ml of hydrazine, which is a reducing agent, in 100 ml of secondary distilled water, and dispersed using a bath sonicator for 1 hour. The mixture was stirred for an additional 24 hours using a stirrer to maintain uniform dispersion of the prepared graphene oxide solution.

4 is an image showing the dispersion stability of a graphene oxide solution to which a reducing agent is added according to an embodiment of the present invention.

Referring to FIG. 4, it can be seen that the stability of the graphene oxide solution decreases as the addition ratio of hydrazine increases relative to the content of graphene oxide. It can be seen that as the addition amount of hydrazine increases, the degree of reduction of the graphene oxide increases and the degree of dispersion in the graphene oxide solution decreases.

5 (a) to 5 (b) are graphs showing results of FT-IR analysis of a graphene oxide solution prepared according to an embodiment of the present invention and a graphene oxide solution added with a reducing agent.

5 (a) to 5 (b), 1 means C = O stretching, 2 means C = C skelectal vibration, and 3 means C-OH stretching. 5 (a) shows FT-IR analysis of a graphite oxide (GO) solution to which no reducing agent is added. As a result, C = O stretching and C-OH peak are clearly observed. In contrast, FIG. 5 (b), which is an FT-IR analysis of a graphene oxide solution containing a reducing agent (hydrazine), shows that the C = O stretching and the C-OH peak are remarkably reduced.

&Lt; Experimental Example 5: Preparation of electrode for lithium secondary battery &

The electrode slurry prepared in Experimental Example 3 was coated on a copper (Cu) current collector and dried.

6 is an SEM photograph showing the result of observing the surface of the electrode according to the ratio of the negative electrode active material and the graphene oxide.

Referring to FIG. 6, it can be observed that as the content of the graphene oxide in the electrode slurry increases, the graphene oxide binder completely covers the negative electrode active material.

&Lt; Experimental Example 6: Preparation of lithium secondary battery &

A 2032 coin cell was fabricated using the electrode prepared in Experimental Example 5 to evaluate the cell. The electrode prepared in Experimental Example 5 was used as a working electrode and lithium metal was used as a counter electrode and ethylene carbonate (EC): diethyl carbonate (LiPF ₆ ) dissolved in 1.3M lithium salt (LiPF ₆ ) DEC) in a volume ratio of 3: 7 was used as the electrolyte.

<Comparative Example>

Except that an electrode slurry is prepared by mixing a silicon-based negative active material made of a Si-Ni-Ti metal alloy with polyacrylamide (PAA) as a polymer binder, and then the prepared electrode slurry is coated on a copper current collector , And a lithium secondary battery was produced under the same conditions as in Experimental Example 6. [

7 (a) to 7 (c) are graphs showing the results of characteristics evaluation of a lithium secondary battery according to an embodiment of the present invention. 7 (a) is a graph showing the first charge / discharge curve, and Figs. 7 (b) and 7 (c) are graphs showing lifetime characteristics.

Referring to FIG. 7 (a), when an electrode slurry containing a graphene oxide is applied to form an electrode, electrostatic capacity is improved compared to when an electrode slurry containing a polymer binder, that is, polyacrylamide is applied .

7 (b), when an electrode slurry containing a graphene oxide is applied to form an electrode, an electrode slurry containing a polymer binder, that is, a polyacrylamide is applied to form a lithium secondary It can be seen that the life of the battery is long. In addition, when the ratio of the active material to the graphen oxide was 90:10, it was found that the electrostatic capacity and the life characteristics were the most excellent.

Specifically, referring to FIG. 7 (c), when the mixing ratio of the active material and the graphene oxide is mixed in a weight ratio ranging from 92: 8 to 88:12, all the electrodes within the above range exhibit similar lifetime characteristics .

The results of the evaluation of the battery life characteristics show that the life characteristics of the battery are improved as the content of the graphene oxide in the slurry of the anode electrode is increased.

While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it is to be understood that the present invention is not limited to the disclosed exemplary embodiments, and various changes and modifications may be made by those skilled in the art without departing from the scope and spirit of the invention. Change is possible.

Claims (11)

Dispersing the graphene oxide in a solvent to produce a graphene oxide solution;
Mixing the graphene oxide solution and the active material to prepare an electrode slurry;
Applying the electrode slurry to a substrate; And
And drying the coated electrode slurry to form an electrode active material layer. The method according to claim 1,
Wherein the graphene oxide comprises an oxygen functional group. &Lt; RTI ID = 0.0 &gt; 11. &lt; / RTI &gt; The method according to claim 1,
Wherein a reducing agent is further added to the graphene oxide solution. The method of claim 3,
Wherein the reducing agent is at least one selected from the group consisting of hydrazine, hydroic acid, and sodium borohydride. The method according to claim 1,
Wherein the slurry does not contain a polymeric binder. The method according to claim 1,
In the step of preparing the slurry by mixing the graphene oxide solution and the active material,
Wherein the active material and the graphene oxide are mixed at a weight ratio ranging from 92: 8 to 88:12. The method according to claim 1,
In the step of forming the electrode active material layer by drying the coated electrode slurry,
Wherein a part of the applied graphene oxide is reduced to form reduced graphene on the surface of the electrode active material layer. Active material, solvent, and graphene oxide,
Wherein the active material and the graphene oxide are mixed in a weight ratio ranging from 92: 8 to 88:12. 9. The method of claim 8,
Wherein the electrode slurry does not contain a polymeric binder. An electrode for an electrochemical device comprising an active material and a graphene oxide binder. 11. The method of claim 10,
Wherein the reduced graphene is formed on at least one surface of the graphene oxide binder.

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